Valve apparatuses are used for the delivery and/or distribution of a wide variety of liquids. Such valve apparatuses may be formed for example as so-called injection valves, in which the opening of an injection nozzle is controlled very precisely by means of a valve needle. By means of a modern injection valve, it is thus possible for even extremely small liquid quantities to be accurately metered. Such accuracy is required for example in internal combustion engines in which fuel is injected at high pressure into the combustion chamber by means of corresponding fuel injectors. Here, the fuel must be supplied in precisely predefined quantities and at predefined times. For the conditioning of the combustion process, the fuel injection valve of a modern internal combustion engine generally performs multiple injections, wherein the fuel quantity used is varied depending on the injection phase. Relatively small fuel quantities are typically injected for the pilot injection, whereas relatively large fuel quantities are delivered into the combustion chamber during the main injection.
The spectrum of fuel quantities required in the individual phases of the fuel injection in an internal combustion engine constitutes an important criterion in the design of a suitable injection valve. For example, the drive device provided for moving the valve needle must be designed to be large enough to ensure the maximum needle stroke required during the main injection. On the other hand, it must also be possible for the valve needle to be controlled quickly and precisely enough to permit an optimum injection of small or extremely small fuel quantities during the pilot injection.
A drive device typically used for deflecting the valve needle therefore has an electric drive means, for example a piezoelectric or electromagnetic actuator. In said drive concept, the actuator acts as a direct drive, wherein the valve needle, owing to mechanical contact with components of the drive, is deflected out of its closed position by directly following the deflection or expansion of the actuator. The direct drive thus permits particularly fast switching times and precise regulability, in particular in combination with closed loop regulation. The switching travel that can be realized in this way is however limited to the maximum deflection of the actuator. In the case of a piezo stack, this is for example only approximately 60 to 70 micrometers. Such a small needle stroke is however not expedient for the delivery of relatively large liquid quantities. To overcome said disadvantage, a more complex construction of the direct drive is required, which manifests itself inter alia in high production costs.
To realize a greater valve needle stroke, use may also be made of hydraulic drive devices. In said drive concept, a hydraulic force which effects the deflection of the valve needle is generated utilizing different pressure conditions within the valve apparatus. In the hydraulic drive activated for example by means of a servo valve, the deflection of the valve needle takes place in the form of ballistic flight, thus permitting a considerably greater needle stroke in relation to the electric direct drive. However, owing to the indirect response of the valve needle to the control, the possibilities for closed loop regulation and thus also a precise injection of extremely small liquid quantities are severely limited with said drive concept.